[Intel-gfx] [PATCH 1/5] drm: Add atomic helper to redo a modeset on current mode

[Daniel Vetter]

On Mon, Oct 24, 2016 at 9:00 AM, Manasi Navare
<manasi.d.navare at intel.com> wrote:
>> I guess we just need to do some additional work on top to make sure the
>> vblank ioctl can't see invalid state. Which would then again make upfront
>> link trainig possible ...
>
> Could you share some more details on what work would need to be done
> for vblank? Then I can investigate it a little bit more tomor during the day.

So the trouble is that drm_irq.c is still from the old pre-kms days.
Which means it deals in int pipe instead of struct drm_crtc *, among
other things. But we can't simply switch over because some old drivers
(pre-kms ones) still depend upon that old code. Hence we need:

1. Duplicate most of the code in drm_irq.c into a new
drm_crtc_vblank.c, which is only used for kms drivers. And in the
ioctl code have a DRIVER_MODESET check and either call the new kms
version (in drm_crtc_vblank.c) or the old one (still in drm_irq.c).

2. Convert the int pipe into a drm_crtc pointer in the new kms code.
For prettiness we could (try) to do that as much as possible.

3. Grab the drm_crtc->mutex in the ioctl code to block these races.

-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch